1. Field of the Invention
The present invention relates to a hologram screen and a method of producing the same. In particular, a first aspect of the present invention relates to a hologram screen for reproducing an image based on an output light obtained by scattering and diffusing an image light which is input from an image projector, and a producing method of the same; a second aspect of the present invention relates to a producing method of a hologram element which can be used as a display apparatus for displaying the image, such as a still image and an animation, by irradiating the image light thereto; a third aspect of the present invention relates to a hologram screen and a producing method of the same; and a fourth aspect of the present invention relates to a hologram screen for reproducing an image based on an output light obtained by scattering and diffusing an image light.
2. Description of the Related Art
A hologram screen, which is formed by a hologram element and a transparent glass, has been widely known in the field of image projecting techniques. A hologram element is of basically two types, i.e., a light-transmitting type and a light-reflecting type and the position of an observer who observes the hologram screen is different in each type.
As representative problems to be solved in a conventional hologram screen, there are the quality of the image, such as unevenness of color and brightness on the hologram screen, cloudiness and a partial non-transparent state on the hologram screen, and the difficulty of preparing very large hologram screen. These problems will be explained in detail with reference to the attached drawings described below.
The first object of the present invention is to provide a hologram screen, which has no unevenness of color on the reproduced image, and a method of producing the screen
The second object of the present invention is to provide a method of producing a hologram screen in which an observer can observe a uniformly bright image without change of brightness and color to a broad extent on the hologram screen.
The third object of the present invention is to provide a hologram screen, which has good reappearance of the reproduced image on the hologram screen and which can realize low cost and easy production of the hologram screen, and a method of producing the screen.
The fourth object of the present invention is to provide a hologram screen which has good transparency and no cloudy state so that the observer clearly and easily observe the back of the hologram screen.
In accordance with a first aspect of the present invention, there is provided a hologram screen, and a method of producing the same, for reproducing an image based on an output light obtained by scattering and diffusing an image light from an image projector, characterized in that; when a white light is used as the image light and projected on the hologram screen; and when a distance between two points at optional two points A and B on a surface of the hologram screen is given by 20 cm or less, and a value of the CIE 1976 chromaticity coordinate (uxe2x80x2, vxe2x80x2) at the point A is given by (uxe2x80x2A, vxe2x80x2A) and the value of the CIE 1976 chromaticity coordinate (uxe2x80x2, vxe2x80x2) at the point B is given by (uxe2x80x2B, vxe2x80x2B); the output light, which is output perpendicularly from the surface of the hologram screen, has a color distribution in which a color difference xcex94uxe2x80x2vxe2x80x2 between two points A and B is derived from the following formula (1) and given by 0.06 or less, where, the formula (1) is expressed by,
xcex94uxe2x80x2vxe2x80x2=[(uxe2x80x2Axe2x88x92uxe2x80x2B)2+(vxe2x80x2Axe2x88x92vxe2x80x2B)2]1/2xe2x80x83xe2x80x83(1) 
Further, the output light, which is output to a viewpoint defined by the following formula (2) from the surface of the hologram screen, has a color distribution in which a color difference xcex94uxe2x80x2vxe2x80x2 between two points A and B is derived from the above formula (1) and given by 0.01 or less, where, the formula (2) is expressed by,
H/2L=0.1xe2x80x83xe2x80x83(2) 
in the formula (2), L is a distance between the viewpoint and a center of the hologram screen, and H is a length of the hologram screen at the direction of the height.
In a preferred embodiment, a spectral characteristic of the output light, which is output perpendicularly from the surface of the hologram screen, has a characteristic in which either a difference between peak wavelengths at the whole of the surface of the hologram screen is given by 120 nm or less, or a difference between half bandwidth is given by 100 nm or less.
In another preferred embodiment, when producing the hologram screen defined in claim 1 or 2 by irradiating the object light and the reference light onto a photosensitive material and by exposing the photosensitive material, the photosensitive material has a thickness distribution which is inclined to an incident direction of the reference light.
In still another preferred embodiment, when an incident angle of the reference light to the photosensitive material becomes larger, the thickness distribution of the photosensitive material becomes thicker.
In still another preferred embodiment, when the thickness at a center of the photosensitive material is T0, and when thickness difference of both ends of the photosensitive material is xcex94T, the following relationship, i.e., xcex94Txe2x89xa60.5T0, is defined.
In still another preferred embodiment, the thickness distribution of the photosensitive material is defined by the following formula (3), i.e.,
T=a(R0xe2x88x92R)+T0, and a=bxc2x7xcex80xe2x88x920.9xe2x80x83xe2x80x83(3) 
where, T is a thickness at an optional point on the photosensitive material, T0 is a thickness at the center of the photosensitive material, R is an incident distance of the reference light at the optional point on the photosensitive material, R0 is the incident distance of the reference light at the center on the photosensitive material, xcex80 is an incident angle of the reference light at the center of the photosensitive material, and xe2x80x9cbxe2x80x9d is a coefficient determined by the thickness of the photosensitive material and given by 0 less than b less than 1.
In still another preferred embodiment, when producing the hologram screen defined in claim 1 or 2 by irradiating the object light and the reference light onto a photosensitive material and by exposing the photosensitive material, ultraviolet light is previously irradiated onto the photosensitive material so as to have an energy distribution which is inclined to an incident direction of the reference light.
In still another preferred embodiment, the energy distribution of the ultraviolet is given by the following formula (4), i.e.,
0.8Exe2x89xa6Euvxe2x89xa61.2E, and E=0.01xc2x7(Rxe2x88x92R0)+E0xe2x80x83xe2x80x83(4) 
where, R is the incident distance of the reference light at the optional point on the photosensitive material, Euv is an amount of energy of the ultraviolet irradiated to the optional point on the photosensitive material, R0 is the incident distance of the reference light at the center of the photosensitive material, and E0 is the amount of energy of the ultraviolet irradiated to the center of the photosensitive material.
In still another preferred embodiment, when producing the hologram screen defined in claim 1 or 2 by irradiating the object light and the reference light onto a photosensitive material and by exposing the photosensitive material, an incident distance of the reference light at an optional point of the reference light is shorter than an incident distance of an image light which is irradiated from an image projector when reproducing the image on the hologram screen.
In still another preferred embodiment, when producing the hologram screen defined in claim 1 or 2 by irradiating the object light and the reference light onto a photosensitive material and by exposing the photosensitive material, an intensity ratio of the reference light and the object light is defined by a relationship of IR/IOxe2x89xa610, on the whole of the surface of the photosensitive material, where, IR is the intensity of the reference light, and IO is the intensity of the object light.
In accordance with a second aspect of the present invention, there is provided a method for producing a hologram screen formed by interfering of a reference light and an object light transmitted through a light diffusion body, and by recording the light diffusion body on a photosensitive material, characterized in that; a mirror is arranged approximately perpendicular to the light diffusion body; the photosensitive material and the light diffusion body are rotated by the same angle xcex8 around an axis which is intersected perpendicularly to a center of the photosensitive material and used as a rotational center; and a polarized direction of a laser light is defined by either P-polarization or S-polarization which is inclined by the angle in the range of xcex8xe2x88x925 to xcex8+5.
In accordance with a third aspect of the present invention, there is provided a hologram screen for reproducing an image based on an output light obtained by scattering and diffusing an image light from an image projector, characterized in that; a half bandwidth of a spectral characteristic of the hologram screen is given by 100 nm or more; a diffusion light which is obtained by a light diffusion body having a large light diffusion angle is used as an object light; a non-diffusion light is used as a reference light; and the object light and the reference light are irradiated on a photosensitive material in order to form an interference fringe so that a hologram element is produced.
In a preferred embodiment, the light diffusion angle of the hologram screen is defined by an angle in which the light diffusion angle of the hologram screen is 10xc2x0 or more.
In another preferred embodiment, a half bandwidth of a spectral characteristic of the hologram screen is given by 100 nm or more; a diffusion light which is obtained by a light diffusion body is used as an object light; a non-diffusion light is used as a reference light; and the object light and the reference light are irradiated on a photosensitive material having the thickness of 1 to 20 xcexcm in order to form an interference fringe so that a hologram element is produced.
In still another preferred embodiment, a peak wavelength of the hologram screen is either 525 nm or less, or 585 nm or more; a half bandwidth of a spectral characteristic of the hologram screen is 100 nm or more; a diffusion light which is obtained by a light diffusion body is used as an object light; a non-diffusion light is used as a reference light; the object light and the reference light are irradiated on a photosensitive material in order to form an interference fringe; and a refractive index of the photosensitive material is adjusted so that a hologram element is produced.
In still another preferred embodiment, the diffusion light which is obtained by the light diffusion body is used as the object light; the non-diffusion light is used as the reference light; the object light and the reference light are irradiated on the photosensitive material in order to form the interference fringe; and a heat treatment is performed for the photosensitive material in the extent of 80xc2x0 to 150xc2x0 C. so that a hologram element is produced.
In still another preferred embodiment, the diffusion light which is obtained by the light diffusion body is used as the object light; the non-diffusion light is used as the reference light; a sum of an exposure intensity of the object light and the exposure intensity of the reference light is defined in the extent of 0.02 to 50 mW/cm2; the object light and the reference light are irradiated on the photosensitive material in order to form the interference fringe so that a hologram element is produced.
In still another preferred embodiment, the diffusion light which is obtained by the light diffusion body is used as the object light; the non-diffusion light is used as the reference light; an intensity ratio (R/O) of the intensity (O) of the object light and the intensity (R) of the reference right is defined by 0.1 to 30; and the object light and the reference light are irradiated on the photosensitive material in order to form the interference fringe so that a hologram element is produced.
In still another preferred embodiment, a peak wavelength of the hologram screen is either 525 nm or less, or 585 nm or more; a diffusion light which is obtained by a light diffusion body is used as an object light; a non-diffusion light is used as a reference light; the object light and the reference light are irradiated on a photosensitive material in order to form an interference fringe; and a thickness of of the photosensitive material is adjusted so that a hologram element is produced.
In still another preferred embodiment, a peak wavelength of the hologram screen is either 525 nm or less, or 585 nm or more; a diffusion light which is obtained by a light diffusion body is used as an object light; a non-diffusion light is used as a reference light; an incident angle xcex8r of the reference light to a photosensitive material is different from an incident angle xcex8e of the image light to the hologram screen; and the object light and the reference light each having the above different angle are irradiated on the photosensitive material in order to form an interference fringe so that a hologram element is produced.
In still another preferred embodiment, an amount of angle correction which indicates a difference between the incident angle xcex8r and the incident angle xcex8e is defined by the extent of xe2x88x925xc2x0 to +5xc2x0.
In still another preferred embodiment, a half bandwidth of a spectrum characteristic of the hologram screen is given by 100 nm or more; a diffusion light which is obtained by a light diffusion body is used as an object light; a non-diffusion light is used as a reference light; and a plurality of object lights each having different angle are irradiated on a photosensitive material in order to form an interference fringe so that a hologram element is produced.
In accordance with a third aspect of the present invention, there is provided a hologram screen for reproducing an image based on an output light obtained by scattering and diffusing an image light from an image projector, characterized in that, a haze ratio is given by 5 to 60%.
In a preferred embodiment, a screen gain of the hologram screen is given by 0.3 or more.
In another preferred embodiment, an intensity ratio ER/EO of the intensity EO of the object light and the intensity ER of the reference light is changed in accordance with a scattering angle of the light diffusion body.
In still another preferred embodiment, when the scattering angle of the light diffusion body is set to a large angle, the intensity ratio ER/EO is set to a small value.